An asteroid that crashed into the earth 65 million years ago may not have been the cause of the dinosaurs‘ extinction, a group of researchers are arguing. Instead, that impact may have been just a prelude to the main event, when a wave of volcanic eruptions spewed out massive clouds of sulfur dioxide, clouding the air and bringing showers of acid rain. The researchers are basing their theory on studies of an area in India called the Deccan Traps, which was convulsed with volcanic activity around 65 million years ago. At least four waves of massive eruptions spread successive sheets of thick basalt across the land for more than 500 miles, and they piled into a plateau more than 11,000 feet high over thousands of years [San Francisco Chronicle].

The new research on the Deccan Traps volcanoes, announced at the ongoing meeting of the American Geophysical Union, are the first major challenge to the asteroid theory that has dominated dinosaur extinction studies for three decades. That theory posits that a six-mile-wide asteroid slammed into Mexico’s Yucatan peninsula, creating the Chicxulub crater and cooling the climate so drastically that the majority of life forms went extinct in what’s known as the Cretaceous-Tertiary (or K-T) extinction. But geologist Gerta Keller and her colleagues argue that the impact occurred well before the massive die-offs began. By examining sediment layers, the team found that the crater impact appears to have occurred about 300,000 years before the K-T boundary, with virtually no effects to biota. “There is essentially no extinction associated with the impact,” Keller said [LiveScience].

Meanwhile, geophysicist Vincent Courtillot determined more exact dates for the Deccan Trap eruptions by studying the magnetic signatures of the Indian volcanic deposits that lined up with the Earth’s magnetic field as they cooled. Because the orientation of the magnetic field has changed over time, lava that cooled at different times will have different signatures. The more than 2-mile thick pile of Deccan Traps deposits has several major pulses that occurred over the course of several decades each, almost certainly less than a hundred years [Wired Science].

The researchers say they detected individual pulses of eruptions at 67.5 and 65 million years ago, with two more quickly following. After the first flow, “the species disappear; we have essentially very few left,” Keller said. The two subsequent flows prevented any recovery, and “by the fourth flow, the extinction is complete,” Keller said [LiveScience]. The researchers also argue that an asteroid impact wouldn’t kick up enough dust and sulfur dioxide to alter the climate around the planet, but says that these supervolcanoes may have spewed 10 billion to 150 billion tons of sulfur dioxide into the air with each pulse of eruptions.

However, the proponents of the asteroid impact theory aren’t going to quietly accept the junking of their thesis. “There was volcanism at the time. There’s always volcanism, but that impact is so significant that you can’t ignore it,” said Rick Firestone of Lawrence Berkeley National Laboratory who studies the link between impacts and extinctions. “The only question is, were there other things that happened as result of it” [Wired Science].

Interesting to say the least. While the argument for the impact model seem pretty good, this adds another twist to it. My biggest fear out of all this is that people who deny science in general will try to use this as some sort of proof of how fallible science is, while forgetting that it was science itself that is the self correcting mechanism at work here.

Rick Dickson

Might the asteroid impact not have caused the Deccan Traps to have erupted? I very much doubt that the dating of both events so long ago can be so precise, so the hundreds of thousands of years between the two might not be an exact time measurement. If the Deccan Traps erupted shortly after the KT impact, it may have been because of the impact event itself. All that pressure and force exerted on a closed system like the earth’s geosphere might have forced up magma in weak areas of the mantle where it was closer to the surface like the Deccan Traps in India. A similar case might be made for the PT (Permian Triassic) extinction event. The eruption of the Siberian Traps occurred at about the same time. There is some evidence also for a meteor/asteroid impact at the PT boundary layer as well. Again the impact of the asteroid might have caused the Siberian Trap eruptions. Therefore, maybe the dinosaurs were killed off by the volcanic eruptions of the Deccan Traps, which themselves were caused by the KT asteroid impact.

D. Cohen

If a big-enough asteroid hit the earth, might not the impact break through the crust resulting in giant lava flows that geologists now regard as the output of a supervolcano? Could the Deccan traps themselves mark the impact site of an asteroid even bigger than Chicxulub? I remember reading that the giant “mare” lava flows on the moon were thought to be the result of asteroid impacts too large to leave behind only a crater.

S huntington

there is an interesting theory about asteroid impacts- it likens it to someone shot in the head- gross-but similar- liquid filled spheres with a hard outer shell- a gunshot makes relatively small entry wounds but leaves a big hole opposite the entry- the theory holds that asteroids would leave a small hole at impact but a big crack from the shockwaves opposite the impact site on the globe- is the indian volcanoe site opposite the yucatan impact site?

Albert Bakker

Yes, the Deccan Traps are largely on the opposite side of the Mexican impact site, but also largely on the same latitude, on the wrong hemisphere in other words. The centre of such a wave would lie in the middle of the Indian Ocean. But that is the way the earth looks like now.

65 million years ago the picture would fit a tiny bit better, Yucatan being a little more to the north and the Deccan Traps being a little bit more to the south. But while you can ignore differences in thickness of the bone to determine where the bullit is going to exit depending on it’s momentum, you cannot ignore differences in the thickness of the Earth’s crust, where things are going to get really hot. And also such a theory would need to take into consideration consequential disturbances in the convection flows inside the mantle, which in turn would have some impact on the earth’s magnetic field, which in turn could have nasty consequences for creatures who aren’t particularly well protected against radiation.
One might favor a coincidence of cumulative effects of a causally linked chain of events over a single culprit.